Method of tanning hides and skins



Patented Apr. 10, 1934 UNITED STATES PATENT OFFICE I METHOD or TANNINGRIDES AND SKINS No Drawing. Application January 12, 1931,

. Serial No. 508,375

11 Claims.

This invention relates to the tanning of hides and skins and moreparticularly to combined tannages involving treatment of the hides andskins with both vegetable and mineral tanning substances.

In accordance with methods heretofore employed in securing combinationtannages of hides and skins, the latter were tanned throughout theirwhole substance when subjected to a mineral tanning material and alsowhen treated with a vegetable tanning material, irrespective of theorder of sequence of the mineral and vegetable tanning operations.Furthermore, in the first tanning operation, whether by mineral or byvegetable tanning matter, no special care was taken of the tender grainsurface of the hide or skin nor any provision made against shrinkage ofthe hide or skin during such tanning operation. For instance, it wascommon, particularly in tanning by mineral substances, to dump a mass ofhides or skins into a drum, the inner surface of which was'provided withprojecting pegs or shelves, and to begin rotation of the drum at oncewithout in any way protecting the tender grain surface of the hides orskins. Furthermore, in such handling of hides and skins there was sureto be very considerable shrinkage which made it impossible to secure thedesired footage, particularly from skins, even though a stretchingoperation was attempted following the completion of the tanningoperation. It is a fact, moreover, that any wrinkled or folded portionof a hide or skin which is tanned in such wrinkled or folded conditioncannot subsequently be made to have the appearance of a fine smoothgrain surface, since such wrinkles or folds persist, to a great extentat least, in spite of treatment intended to obviate them.

Objects of the invention are to speed up the tanning of hides and skins,to obtain a better product, and, in the case of skins particularly, tosecure greater area in the finished leather than has been possible bythe methods previously employedin combination tanning.

To these ends, and in accordance with an important characteristic of theinvention, a hide or skin is first treated with an inorganic substancesuch as a mineral tanning material capable of rapid penetration, theapplication of the tanning material being made while the hide or skin isspread out or stretched in extended condition upon a supporting surface,the hide or skin being maintained in such spread out or stretched outcondition for a time substantially just suflicient to insure such a setto the fibers of the hide or skin that the latter will maintain itsextended area when later subjected to treatment by tanning substancesinother operations, such as that of drumming, designed to complete thetanning of the hide or skin. By mineral tanning 6O material is meanttanning material of other than vegetable or animal origin. Convenientlya chromium tanning compound is applied to the grain surface of a hide orskin while the latter is in spread out ,or stretched out condition, theadvantages being that the chromium compound quickly gives the tendergrain surface a protective tanning and also penetrates into the hide orskin with relatively great rapidity so that the latter may be removedfrom its supporting surface after a relatively short time has elapsedwithout danger of any substantial amount of shrinkage taking place. Inthe case of a thin skin the treatment may take only a few minutes whilein the case of heavy hides as much as an hour or two may be required.Following the desired set of the fibers of a hide or skin the latter maybe subjected to tanning operations with vegetable tanning agents whilein extended condition on a supporting surface. Preferably, however, thehide or skin, with many others which have received like preliminarytreatment, is thrown into a drum having a strong or concentratedsolution of one or more vegetable tanning substances, and the drummingcontinued until tanning is completed. a 35 In the practice of the methodof tanning hides and skins according to this invention, a hide or skinwill be spread out in extended condition upon a smooth supportingsurface with the grain surface facing upwardly and exposed to theatmosphere. In the case of both hides and skins, a large portion(substantially half, more rather than less) of the watery content ofeach hide or skin will be removed either manually or by the use of asuitable machine either before spreading the hide or skin out on a worksupport or simultaneously with the spreading out operation. Thestretching out of the skin and the removal of water therefrom isconveniently accomplished at one operation by slicking the skin out on asmooth supporting surface. In the case of skins, as distinguished fromhides, each skin will be stretched out in fully extended condition onthe work support before the application of any tanning material so thatthe full area of the skin may be obtained in the finished leather. Inthe case of hides, it is essential that each hide be spread out toremove all wrinkles and folds but it is not necessary to employstretching operations since the leather made from hides isrelawell-known Martin Dennis solution tively thick and heavy and is soldby the pound and not by the square foot, as is the case with lightleathers made from skins. The new and improved method of tanning whichinvolves the spreading or stretching out of the hide or skin upon asupporting surface, and the removal of a large proportion or, in somecases, the larger portion, of the watery content of a hide or skin,prior to any tanning of the hide or skin, and also the maintenance ofthe hide or skin in spread out or stretched out condition until the hideor skin has set in such extended condition, is described and claimed inmy copending application Serial No. 402,319, filed October 24, 1929, andhence will not be claimed herein. In the step of preliminarily tanningthis spread out or stretched out hide or skin from which the desiredamount of water has been removed, a strong basic chrome tanning liquor,for instance, the (United States Patent No. 511,411, December 26, 1893)is applied to the exposed surface. It is to be understood, however, thatthe method herein described is not limited to the use of chrome or othermineral salts, since organic substances,

' such as formaldehyde, may be employed. In the case of a relativelylight skin one application only is needed, whereas with heavier skins orhides several applications may be required and allowed to act until thehide or skin fibers have been tanned to a sufficient depth to insurethat the hide or skin will maintain its smooth grain sur-- face and itsextended area upon subsequent treatment. The hide or skin may then befinished, before any substantial drying thereof has taken place, by oneor more applications of a strong or concentrated solution of a vegetabletanning material either while it is stationary upon a work supportingsurface or by introducing it into a vat or drum. By concentratedsolution is meant one of a strength not substantially less than 100 Bkr.and by a strong solution one of a strength less than 100 but notsubstantially less than Bkr.

In the case of hides intended particularly for soles of boots and shoes,vegetable tanning of the hide secures a better quality of leather forthe purpose intended than does mineral tanning, since such leather isfirmer and of better appearance, although less resistant to thesoftening action of water. On the other hand chrome sole leathers aremore durable than vegetable ondly, a complete tanning with suitablevegetable extracts. Occasionally this order of mineral and vegetabletanning is reversed but always to meet special requirements in theleather thus produced. The present method involves the application of amineral tanning compound to one surface or to both surfaces of a hide orskin to tan and thus preserve the tender grain surface thereof, thetanning being continued for such length of time only as will securesetting of the hide or skin in its extended area. Preferably thepreliminary tanning will be secured by an application of the tanningmaterial to the grain surface to secure a finely tanned grain surfacenot subject to injury even when subsequently subjected to the relativelyrough tanning operation of drumming. In applying the mineral tanningsubstance to both surfaces of the hide or skin, the latter must bespread out or slicked out twice upon a work supporting surface withfirst one surface and then the other exposed for treatment, as disclosedin said prior application.

After the hide or skin has been allowed to remain on the supportingsurface with the chrome liquor applied thereto for the desired length oftime, the hide or skin is preferably introduced with many others, whichhave received like treatment, into a drum containing a strong tanningsolution of one or more vegetable extracts. The drumming of the hides orskins is continued until thorough penetration of the hide or skin issecured. The hides or skins are then removed and finished in theordinary manner.

Having described my invention, what I claim as new and desire to secureby Letters Patent of the United States is:

1. That improvement in methods of tanning hides and skins whichcomprises spreading a hide or skin out in fully extended condition upona supporting surface, applying a mineral tanning agent to the hide orskin while in extended condition, permitting it to act for a timesubstantially just suflicient to secure setting of a hide or skin in itsspread out condition, and then subjecting the hide or skin to treatmentwith a tanning agent until it is thoroughly tanned throughout.

2. That improvement in methods of tanning hides and skins whichcomprises spreading a hide or skin out in fully extended condition upona work supporting surface, applying a tanning solution of a chromiumsalt to the hide or skin while in extended condition, permitting thetanning solution to act for a time substantially just sufiicient tosecure such a set to the fibers of the hide or skin as will maintain thelatter in spread out condition, and while still moist subjecting thehide or skin to treatment with a solution of a vegetable tanning agentto complete the tanning operation.

3. That improvement in methods of tanning hides and skins whichcomprises applying -a strong solution of a mineral tanning agent to bothsurfaces of a hide or skin, permitting the mineral tanning agent tooperate fora time substantially just sufficient partially to tan thehide or skin to secure setting of the fibers of the hide or skin to anextent sufficient to subsequent shrinkage thereof, and subsequentlysubjecting the hide or skin to treatment with a solution of a vegetabletanning agent to complete the tanning operation.

4. That improvement in methods of tanning hides and skins whichcomprises applying a strong solution of a mineral tanning agent to theflesh side of a hide or skin, permitting the mineral tanning agent tooperate for a time substantially just sufilcient to secure the minimumsetting of the fibers of the hide or skin which will maintain the areathereof, and subsequently drumming the hide or skin in a solution of avegetable tanning agent to complete the tanning operation.

5. That improvement in methods of tanning hides and skins whichcomprises applying a strong solution of a mineral tanning agent to thegrain side of a hide or skin, permitting the mineral tanning agent tooperate for a time sub stantially just suflicient to secure tanning ofthe grain surface and such setting of the fibers of the hide or skin aswill serve to maintain the area thereof, and subsequently drumming thehide or skin in a solution of a vegetable tanning agent.

6. That improvement in. methods of tanning hides and skins whichcomprises applying a strong solution of a mineral tanning agent to ahide or skin, permitting the mineral tanning agent to operate for a timesubstantially just sufficient to secure taming of the grain surface andsubstantially the'minimum setting of the fibers of the hide or skinwhich will serve to maintain the area thereof, and subsequently drumming the hide or skin in a solution of a vegetable tanning agent tocomplete the tanning operation.

7. That improvement in methods of tanning hides and skins whichcomprises stretching a hide or skin out in fully extended condition upona supporting surface, applying a mineral taming agent to the hide orskin while in fully extended condition, permitting it to act for a timesuflicient to secure setting 01 the hide or skin in its spread outcondition, and then subjecting the hide or skin to treatment with asolution of a vegetable tanning agent.

8. That improvement in methods of tanning hides and skins whichcomprises stretching a hide or skin out, in fully extended conditionupon a supporting surface, applying a tanning solution of a chromiumsalt to the hide or skin while in fully extended condition, permittingthe tanning solution to act for a time sufficient to secure tanning ofthe grain surface of the hide or skin and such a set to the fibers ofthe hide or skin that they will maintain the latter in spread outcondition, and before any substantial drying thereof has taken placedrumming the hide or skin in a solution of a vegetable taming agent tocomplete the tanning operation.

9. That improvement in methods of tanning hides and skins whichcomprises applying a solution of an inorganic tanning agent to a hide orskin, permitting said tanning agent to operate for a time substantiallyjust suflicient to secure tanning of the grain surface but no moresetting of the fibers of the hide or skin than is necessary to maintainthe area thereof, and subsequently drumming the hide or skin in asolution of a vegetable tanning extract to complete the tan- .ningoperation.

10. That improvement in methods of tanning hides and skins whichcomprises slicking a hide or skin out in fully extended condition upon asupporting surface, applying a rapidly penetrating mineral tanning agentto the hide or skin while in fully extended condition, permitting it toact for a time sufl'icient to secure setting of a hide or skin in itsspread out condition, and then'subjecting the hide or skin to treatmentwith a strong solution of a vegetable tanning extract.

11. That improvement in methods of tanning hides and skins whichcomprises slicking a hide or skin out in fully extended condition upon asupporting surface, applying a tanning solution of a chromium salt tothe hide or skin while in fully extended condition, permitting thetanning solution to act for a time sufficient to secure tanning of thegrain surface of the hide or skin, and such a set to the fibers of thehide or skin that they will maintain the latter in spread out condition,and subsequently drumming the hide or skin in a solution of a vegetabletanning extract to complete the tanning operation.

MATTHEW M. MERRII'I'.

